Getting your period every month can be a pain (literally). Another month, another week doubled over in pain from cramps, another craving for an abnormal amount of chocolate. And then, suddenly, your period decides to go rogue and switch things up — and that can be downright terrifying. (Pregnant? Cancer? Dying? All of the above!?)

But despite what your cursory Google searches might tell you, a shifty cycle likely isn't a sign of any of those things (whew!), it's just that you're getting older (oh...), according to Alyssa Dweck, M.D., a practicing OB/GYN and assistant clinical professor of obstetrics and gynecology at Mount Sinai School of Medicine. "There's an unspoken rule among doctors that a woman's period tends to change through the decades," she says. "Your cycle is often an indicator of what's going on in your health and in your life, and there are many transitions between your twenties, thirties, and forties."

Your period hinges on hormones (they're released, head to your ovaries, and kick off a series of events that eventually cause your uterine lining to shed — ahem, your period), so anything that can cause them to go screwy, like stress, lifestyle changes, health conditions (so, basically everything) can disrupt or alter your flow. And likewise, your period can also give you a clue as to what's going on with your body.

In Your 20s...

Ah, those formative years. Just like how you change a lot in your twenties (eating mac 'n' cheese for every meal stops cutting it somewhere around 25...), your period changes, too. Sometimes, it can mean things about your health; other times, not so much.

For one, if you're starting a new birth control —like an IUD, for example — there's a chance it could change your period from how it was in your teens. "Depending on the type you're using, starting a new birth control method can lighten your flow, or make it non-existent," Dweck says. That's not something to stress about.

Speaking of stress, though, that can be a major factor, as stress hormones disrupt the signal from your brain to your ovaries. Sure, there are changes at every stage of life, but there are lots of monumental things that tend to happen in your twenties — tackling your first job, then losing that job, getting into a serious relationship, then getting out of it. All of those things can affect your period. An erratic period can't always be attributed to stress, but Dweck says it's the cause of erratic periods for many women in their twenties.

But if you're not stressed out and you're suddenly having erratic cycles where your period lasts forever or goes MIA for months (and you're not pregnant), you may have PCOS, a hormonal imbalance that causes what looks like a string of small cysts to grow on your ovaries. It tends to show up in women in their twenties, although you can be diagnosed with it at any time. "For some reason, we're seeing an uptick in cases of this," Dweck says. "We're not exactly sure why." Along with super random periods, other signs of PCOS are excess facial hair growth and acne.

If your period pulls a complete vanishing act (and you're not pregnant or dealing with PCOS), that could signal a few things. It may stop entirely if you're severely underweight, severely overweight, or if you're dealing with a thyroid disorder (which, Dweck notes, can also cause periods to get much heavier). There are treatment options, so it's important to see your doc.

In Your 30s...

"Periods can be indicators of your health, and your thirties tend to be a time when some benign health conditions pop up," Dweck says. Some of the most common: fibroids, polyps and benign uterine growths. All can be treated, but could be interfering with your period, making it heavy and painful.

Also at play in your thirties is...dun dun dun....having kids. If you have a baby in your thirties, it can also affect your cycle. It can take time for things to get back to normal, especially if you're breastfeeding. And it's not just actually being pregnant, but trying to get pregnant (stress) — or if you've suffered a miscarriage, that can cause irregular or missed periods, Dweck says.

In Your 40s...

Nothing lasts forever, including your period. But chances are, you probably hear the word menopause and are like, "What? Me? No! Not so fast"' But actually, "perimenopause-type changes can start up to 10 years before actually starting menopause," Dweck says. "With this, you can expect to see some fluctuations in your period, either missing one every now and then or getting a longer period."

You have your hormones to thank for that. When you're younger, the levels of two hormones — estrogen and progesterone — wax and wane over the course of your menstrual cycle. Once you approach menopause, these hormones stop following their normal patterns, triggering changes in your cycle, according to the American College of Obstetricians and Gynecologists.

Menopause aside, there are other things to watch out for. If you used to think that sweat sessions straight-up sucked, but decided to start hitting up the gym for your big 4-0, that may actually cause your period to go MIA. Changes in exercise routines definitely affect your period, Dweck says. This can happen at any time in your life, but many women who haven't been active for most of their lives tend to decide to incorporate exercise into their lives at this point.

And sometimes, in your 40s, changes in your period can mean something much more serious. "Uterine cancer is something that can come up," Dweck says. "Keep in mind, this is an extreme rarity, however, it's not uncommon to find a pre-cancerous cell that could be causing a problem with your periods around this time in your life." If your periods are getting really weird — extremely abnormal or super heavy — it's time to talk to your doctor.

In Your 50s (and Beyond) …

Medically speaking, you've reached menopause once your period has stopped showing up for a full year. If you begin experiencing bleeding after menopause, that's major cause for concern.Give your doctor a call ASAP.

What to Watch for No Matter How Old You Are

Although there's no such thing as a "typical" period, most women's cycles occur every 21 to 36 days, and lasts anywhere from a few days to a full week.

That said, your cycle isn't going to arrive like clockwork every month, and that's OK, but there are some things that are worth a visit to your doctor (aside from some of the items mentioned above). Mainly, if you haven't had a period in over three months, if you have raging PMS, your cramps are debilitating, you have spotting or heavy bleeding between periods, or your periods are so heavy you have to change your pad or tampon every hour.

If you're someone who has always had painful periods, know that your cycle should actually get less painful over time. If you experience the reverse, give your doctor a ring. And remember to tell your gyno exactly what's really going on so she can treat you properly.